Density functional theory studies of the uncatalysed gas-phase oxidative dehydrogenation conversion of n-hexane to hexenes

Publication date: 15 August 2017 Source:Computational and Theoretical Chemistry, Volume 1114 Author(s): N.E. Damoyi, H.B. Friedrich, H.G. Kruger, D. Willock Density Functional Theory (DFT) modelling studies were conducted for the activation of n-hexane in the gas-phase under experimental conditions of 573, 673 and 773K. The aim of the study was to establish the most favourable radical mechanism for the oxidative dehydrogenation (ODH) of n-hexane to 1- and 2-hexene. Modelling of the 3-hexene pathway was omitted due to absence of this product in laboratory experiments. Computations were performed using GAUSSIAN 09W and molecular structures were drawn using the GaussView 5.0 graphics interface. The B3LYP hybrid functional and the 6-311+g(d,p) basis set were utilized for all the atoms. The most kinetically and thermodynamically favourable pathways are proposed based on the determination of the relative total energies (ΔE#, ΔE, ΔG# and ΔG) for the different reaction pathways. The initial C-H activation step is β-H abstraction from n-hexane (C6H14) by molecular oxygen (O2) to form the alkoxy ( C 6 H 13 O ) and hydroxyl ( OH ) radicals. This is proposed as the rate-determining step (RDS) with the calculated ΔE# =+42.4kcal/mol. Two propagation pathways that involve, separately, the C 6 H 13 O and OH radicals may lead to the formation of 2-hexene. In both the propagation pathways, the C 6 H 13 O and OH radicals activate fu...
Source: Computational and Theoretical Chemistry - Category: Chemistry Source Type: research